DIY 1.5V FM Transmitter Circuit Using BC547 Transistor

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To make an FM Transmitter you do not need to have much knowledge, we just need a transistor and some components, so let's see how it is made.

Components Required

• BC547 Transistor or 2N3904 Transistor
• 22pF Capacitor
• 47pF Capacitor
• 102pF Capacitor
• 100k Resistor
• 4.7k Resistor
• Antenna (any wire or copper wire)
• Copper coil (4 turns)
• 1k Potentiometer
• 1uF 16V Capacitor
• Audio Jack Wire
• 1.5V Battery
• Soldering Iron & Wire

Step-by-Step Instructions

1. Prepare the Components: Gather all the components listed above. Make sure your soldering iron is heated up and ready to use. And you can also make it without a PCB board.

2. Connecting the Coil and Capacitor

• Connect one end of the copper coil to the first pin of the BC547 transistor.

• Connect one end of the 22pF capacitor to the second pin of the transistor and the other end of the capacitor to the first pin of the transistor.

3. Adding the Resistor

   • Solder the 4.7k resistor to the second pin of the transistor. Connect the other end of the resistor to the second end of the copper coil and the first end of the 22pF capacitor.

4. Connecting Additional Capacitors

   • Solder the 47pF capacitor to the first pin of the transistor. Connect its other end to the third pin of the transistor.

   • Solder one end of the 102pF capacitor to the second pin of the transistor. Connect its other end to the middle pin (wiper) of the 1k potentiometer.

5. Connecting the Potentiometer

   • Solder one of the outer pins of the potentiometer to the third pin of the transistor.

   • Solder the middle pin (wiper) of the potentiometer to the negative terminal of the battery.

6. Adding the Capacitor and Resistor

   • Solder the positive pin of the 1uF 16V capacitor to the second pin of the transistor.

   • Solder the negative pin of the capacitor to one end of the 100k resistor. Connect the other end of the resistor to the audio jack.

7. Connecting the Audio Jack

   • Solder one wire from the audio jack to the free end of the 100k resistor.

   • Solder the other wire from the audio jack to the middle pin (wiper) of the potentiometer. Learn more about audio jack.

8. Adding the Antenna

   • Solder a piece of copper wire to the first pin of the transistor to serve as an antenna.

9. Connecting the Battery

   • Connect the positive terminal of the 1.5V battery to the first pin of the transistor and the second ends of the copper coil and 22pF capacitor.

   • Connect the negative terminal of the battery to the middle pin (wiper) of the potentiometer.

Circuit Diagram 1 

BC547 circuit diagram

Testing the Circuit

To test your FM transmitter

1. Insert the 1.5V battery into the circuit.

2. Plug the audio jack into your phone or audio source and play some music.

3. Turn on an FM radio or the FM radio app on your phone.

4. Scan through the FM channels to find the one broadcasting your music.

Circuit Diagram 2 

2n3904 circuit diagram

Troubleshooting Tips

If the transmitter does not work:

• Adjust the position of the copper coil and the antenna to ensure proper connection and signal transmission.

• Double-check all connections and solder joints to ensure there are no loose connections.

People also ask

How can I increase the range of my 1.5V FM transmitter?

To increase the range of your FM transmitter, you can try the following.

• Use a longer antenna. A simple copper wire can be extended to improve transmission.

• Ensure all connections are secure and solder joints are strong to minimize signal loss.

• Use a higher quality coil with more turns for better inductance.

• Increase the power supply voltage slightly, but be cautious not to exceed the voltage rating of the components.

What should I do if my FM transmitter is not broadcasting any audio?

If your FM transmitter is not broadcasting audio, check the following.

• Verify that all components are connected correctly as per the circuit diagram.

• Ensure the audio source (like your phone) is properly connected to the audio jack and that the volume is turned up.

• Check the battery voltage to ensure it is providing sufficient power to the circuit.

• Inspect all solder joints for cold solder or loose connections that might interrupt the signal flow.

Why is my FM transmitter broadcasting a lot of static noise?

If your FM transmitter is broadcasting static noise, try these solutions

• Ensure the antenna is properly positioned and not touching other components, which could cause interference.

• Check for any loose connections or poorly soldered joints that might be introducing noise.

• Move the transmitter away from other electronic devices that could be causing interference.

• Adjust the positions of the capacitors and the coil slightly to fine-tune the frequency and reduce static.